function GunFn(){
	this.bdy = document.documentElement||document.body;
	this.top = document.documentElement.scrollTop||document.body.scrollTop;
	this.box = document.getElementById('mengban');
	this.mb = document.getElementById('mb');
}
GunFn.prototype.init = function(){
	var that = this;
	window.onscroll = function(){
		console.log(that.top);
		if (that.top <= 10) {
			that.box.style.top = 325 + "px";
			that.mb.style.top = -350 + "px";
		}
	}
}
var gundong = new GunFn();
	gundong.init();